The capability of a receiving system to receive low level signals is limited by the ratio (G/T) of the receiving antenna, where (G) is antenna gain and (T) is system noise temperature. While much progress has been made in low noise receiver technology, applications exist in which the antenna gain (G) becomes the limiting factor.
Large high gain antennas are expensive. One alternative to a single high gain antenna is to coherently combine a number of smaller antennas to attempt to achieve comparable performance. In theory, the gain of a coherently combined array of N antennas equals N times the gain of a single antenna element assuming each antenna in the collection has identical characteristics. However, a challenge of this alternative array approach is that the antenna elements must be coherently combined to achieve the desired gain performance.
The coherent combination of multiple antennas has requirements to properly compensate for the differences in arrival time of the signals at each antenna element and to compensate for the insertion phase differences among the individual antenna elements. Past work has identified the required tolerances in such coherent combining and these tolerances depend on the bandwidth of the signals. See, K. M. SooHoo and R. B. Dybdal, “Tolerances for Combining High Gain Antennas,” 1994 IEEE AP-S Symposium Digest, Seattle Wash. pp 209-212, Jun. 19-24, 1994; R. B. Dybdal and K. M. SooHoo, “Arraying High Gain Antennas,” 2000 IEEE AP-S Symposium Digest, Salt Lake City Utah, pp 198-201, Jul. 16-21, 2000.
It would be helpful to be able to provide a method for coherently combining the individual antennas in an array with a large number of antenna elements, in particular in cases where a relatively large bandwidth is required.